If you think someone got into your router and changed settings then go into it write down settings you need for any port forwardings etc, perform a hardware factory reset of the router. Change the default password of the router so that others should be locked out of its configuration. Then go in and make it specific configuration to your needs.
The :80 at the tail end of the IP address is just telling it to use port 80. This port is the most commonly used port for internet outbound. Calling the IP address without port 80 designation should bring you to the same result.
Additionally dont have a open wifi, set the wifi to be secured and use a different key than that of what you had prior.
This should keep them out unless your router was rooted and has a backdoor to gain access to it with a altered BlackHat flash ROM programmed onto it. I have doubts that your issue is this deep.
If your router is a linksys you might want to check to make sure its not a vulnerable model to be targeted for a flaw:
http://www.pcworld.com/article/2098160/worm-themoon-infects-linksys-routers.html